Re: [MMUSIC] SCTP question: Where does it multiplex?
"Dan Wing" <dwing@cisco.com> Tue, 11 December 2012 19:25 UTC
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From: Dan Wing <dwing@cisco.com>
To: 'Paul Kyzivat' <pkyzivat@alum.mit.edu>
References: <5093A2C9.9040001@alvestrand.no> <50B9E3ED.6010604@ericsson.com> <50BA19F9.4040701@alvestrand.no> <50BD04D2.7090207@alum.mit.edu> <50C6F800.1080500@ericsson.com> <50C7548C.3090807@alum.mit.edu> <010401cdd7d0$d006d310$70147930$@cisco.com> <50C786C8.2010403@alum.mit.edu>
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Date: Tue, 11 Dec 2012 11:25:31 -0800
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Subject: Re: [MMUSIC] SCTP question: Where does it multiplex?
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> -----Original Message----- > From: Paul Kyzivat [mailto:pkyzivat@alum.mit.edu] > Sent: Tuesday, December 11, 2012 11:17 AM > To: Dan Wing > Cc: mmusic@ietf.org > Subject: Re: [MMUSIC] SCTP question: Where does it multiplex? > > Hi Dan, > > Comments inline > > On 12/11/12 1:53 PM, Dan Wing wrote: > >> -----Original Message----- > >> From: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] On > >> Behalf Of Paul Kyzivat > >> Sent: Tuesday, December 11, 2012 7:43 AM > >> To: mmusic@ietf.org > >> Subject: Re: [MMUSIC] SCTP question: Where does it multiplex? > >> > >> More inline. > >> > >> On 12/11/12 4:08 AM, Salvatore Loreto wrote: > >>> Hi Paul, > >>> > >>> see in line! > >>> > >>> On 12/3/12 10:00 PM, Paul Kyzivat wrote: > >>>> Commenting on a different point > >>>> > >>>> On 12/1/12 9:53 AM, Harald Alvestrand wrote: > >>>> > >>>>> The interesting difference is that the multiplexing between > >>>>> DTLS/SCTP traffic and BUNDLE multiplexing is that DTLS/SCTP > >>>>> traffic is not carried in SSRCs, which means: > >>>>> > >>>>> - There can be only one DTLS/SCTP stream in a bundle (which may > >>>>> have multiple associations, as you state below); you can't have > >>>>> multiple lines with proto DTLS/SCTP in a bundle. > >>>> > >>>> I am not an SCTP expert. But IIUC, SCTP was designed to run > >>>> directly over IP. It has its own notion of port used to demux > >>>> multiple SCTP associations over the same IP address. > >>>> > >>>> I presume that that same mechanism is still there when SCTP is run > >>>> over DTLS over UDP. > >>>> > >>>> So, the traffic coming over DTLS must first be demuxed into RTP > >>>> traffic and SCTP traffic. > >>> based on the current stack the SCTP traffic is the only traffic that > >>> runs directly over the DTLS stack. > >> > >> Yes, that is what I thought. But Harald has been asking about > >> multiplexing this with RTP traffic. (Actually I think it would be > >> DTLS/SRTP traffic that it would be multiplexed with.) > >> > >>> What I am trying to do is to include the Randell Jesup (I am > >>> including him in CC as I am not sure he is subscribed to this > mailing list) > >>> suggestion to give the possibility to have multiple SCTP > >>> *associations* running on top of the same DTLS session and of > >>> course providing a way to signal it in SDP. > >> > >> IIUC, SCTP (having been designed as a transport layer protocol) > >> defines its own notion of port, and has fields in its protocol to > >> carry the local and remote port number. Presumably those fields are > >> still there when run over UDP or DTLS. So it should be possible to > >> support multiple SCTP associations over the same DTLS connection, > >> each distinguished by its own port pair. > > > > Yes, SCTP has its own notion of ports. How this works when SCTP is > > carried over UDP is not quite clear, especially because SCTP assumes a > > NAPT will not rewrite the SCTP port number (SCTP endeavors to make > > such port rewriting difficult). But of course a NAPT (and the MAP > > techniques) rewrite UDP port numbers. I believe SCTP would only be > > able to successfully convey its UDP port numbers for a device that is > > not behind a NAT (that is, a server sitting directly on the Internet, > > rather than a remote peer that is behind a NAT). Creative use of PCP, > > NAT-PMP, or UPnP IGD would improve that situation in the future. > > I find what you say above confusing. It is confusing, because SCTP's specifications require different things of a NAPT than UDP, TCP, or DCCP. Specifically, SCTP's specifications require the NAPT to not rewrite (not change) the source port number of outgoing SCTP-over-IP packets. Reference draft-ietf-behave-sctpnat. > SCTP running naked over IP would still have its own ports. > If that ran over a path with a NAPT, then I could see why the NAPT might > want to do the same as it does with UDP and TCP, and so replace > addr/port pairs to minimize addr usage. (That's if the NAPT supported > SCTP at all - I gather most don't.) I am not aware of any shipping NAPT that supports SCTP. > But with SCTP over DTLS over UDP, there is a UDP port, and then > presumably a separate SCTP port carried in the SCTP protocol within the > UDP message. Right. And the new SCTP_REMOTE_UDP_ENCAPS_PORT socket option has some relationship, but I do not understand how it works. Reference draft-ietf-tsvwg-sctp-udp-encaps. > An NAPT on the path would presumably be messing with the UDP port. Given > use of DTLS, the NAPT won't even be able to tell that SCTP is being > used, much less mess with the SCTP port. Right. > >> That of course depends on having a signaling mechanism to set it up. > > > > After the initial SCTP association is created, SCTP could be allowed > > to do its own thing (that is, chose to find and use other ports). > > Here you are talking about finding and using other UDP addr/port pairs? Yes, for mobility. > That is explicitly excluded in the DTLS/SCTP mapping. I am thinking about where to layer mobility and multipath for RTP (MPRTP) and for SCTP. Do we do that with MICE (draft-wing-mmusic-ice-mobility) or does SCTP do mobility itself? If we do it with MICE, we need to disable or prevent SCTP from adding / removing interfaces itself, which is why SCTP includes its own ability to signal IP addresses and ports in SCTP itself. -d > Thanks, > Paul > > > SCTP's behavior in this regard is similar to MPRTP (multipath RTP), > > but of course they are not identical. > > > >>> to be clear: at moment WebRTC allows only one SCTP association per > >>> PC, so this is something that would be nice to define just to be > >>> ready for the future. > >> > >> AFAIK WebRTC is just one possible user of this mechanism. The SDP > >> mechanism shouldn't be limited by the constraints of WebRTC. It would > >> be very difficult to define the SDP so that it was impossible to set > >> up multiple SCTP associations over different 5-tuples. > >> > >>>> Then the RTP traffic can be demuxed based on SSRC, and SCTP traffic > >>>> can be demuxed based on SCTP port. And once the traffic for a > >>>> single SCTP port is identified, it can be demuxed based on stream > number. > >>>> > >>>> Representing this in SDP is a challenge. Some variant of the bundle > >>>> proposal might allow bundling together several RTP m-lines and some > >>>> DTLS/SCTP m-lines. This would require a mechanism for specifying > >>>> the SCTP port number - already an open issue (#3) in > >>>> draft-ietf-mmusic-sctp-sdp-02. > >>> I agree that it is a challange how then to bundle everything > >>> together > >> > >> But it is a challenge that needs to be tackled if we are to realize > >> Harald's dream. > > > > -d > > > > > >
- [MMUSIC] SCTP question: Where does it multiplex? Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Salvatore Loreto
- Re: [MMUSIC] SCTP question: Where does it multipl… Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Christer Holmberg
- Re: [MMUSIC] SCTP question: Where does it multipl… Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Markus.Isomaki
- Re: [MMUSIC] SCTP question: Where does it multipl… Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Markus.Isomaki
- Re: [MMUSIC] SCTP question: Where does it multipl… Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Christer Holmberg
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Salvatore Loreto
- Re: [MMUSIC] SCTP question: Where does it multipl… Markus.Isomaki
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Harald Alvestrand
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Dan Wing
- Re: [MMUSIC] SCTP question: Where does it multipl… Dan Wing
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Dan Wing
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Paul Kyzivat
- Re: [MMUSIC] SCTP question: Where does it multipl… Dan Wing
- Re: [MMUSIC] SCTP question: Where does it multipl… Randell Jesup
- Re: [MMUSIC] SCTP question: Where does it multipl… Matthew Kaufman
- Re: [MMUSIC] SCTP question: Where does it multipl… Dan Wing
- Re: [MMUSIC] SCTP question: Where does it multipl… Dan Wing
- Re: [MMUSIC] RESTART: SCTP question: Where does i… Paul Kyzivat
- Re: [MMUSIC] RESTART: SCTP question: Where does i… Dan Wing
- Re: [MMUSIC] RESTART: SCTP question: Where does i… Paul Kyzivat
- Re: [MMUSIC] RESTART: SCTP question: Where does i… Dan Wing
- Re: [MMUSIC] RESTART: SCTP question: Where does i… Paul Kyzivat